In U.S. Pat. No. 4,708,681 issued Nov. 24, 1987 to L. E. Branovich, G. L. Freeman, and B. Smith, for "Method of Making A Long Lived High Current Density Cathode from Tungsten and Iridium Powders," and assigned to a common assignee, a long lived high current density cathode is made from a mixture of tungsten and iridium powders by processing the mixture of powders with an activator into a porous billet, and then impregnating the billet with a chemical mixture of barium oxide, strontium oxide, and aluminum oxide by firing the billet in a dry hydrogen furnace at a temperature at which the impregnant melts.
Though the cathode made by the method of U.S. Pat. No. 4,708,681 gives desirable current densities, it would be desirable to provide a cathod with even better emission characteristics.